1. Field of the Invention:
The present invention relates to an A-shaped evaporator and more particularly to an evaporator A-coil as applied to central air conditioning systems as the indoor half of a split system with the coil being in series with the air moving device of the system. The A-coil evaporator in common practice is an assembly including two evaporator slabs that are conveniently interconnected as part of the complete refrigeration system.
2. Description of the Prior Art:
It is common to design the compressors and evaporators used in air conditioning systems according to the maximum load to which they may be subjected, and it is known in the art to reduce compressor capacity under low load conditions and to make a corresponding reduction in the evaporator surface in service. The effects of reducing the evaporator surface under these conditions is to reduce the evaporator temperature to a useful level for air conditioning and to maintain a sufficient rate of refrigerant flow for proper oil return to the compressor. By reducing the evaporator surface under low load conditions, the compressor output can be reduced accordingly to prevent excessive pressure in the evaporator. U.S. Pat. No. 2,332,981 discloses a refrigeration system wherein selected portions of an evaporator are connected to distributors which are selectively closed to remove portions of the evaporator tube surfaces from service during low load conditions. A serious drawback of multi-circuit evaporators currently used is that in many instances poor humidity control results as the evaporator circuits remaining in service are not capable of maintaining a temperature level sufficient to effectively control humidity.
Other prior attempts such as that disclosed in U.S. Pat. No. 3,866,439 provide an evaporator which comprises a plurality of refrigerant circuits connected to a plurality of distributors. The distributors being connected to the circuit in alternative ways to effect alternative refrigerant flow paths through the evaporator. Selective circuits are withdrawn from service to reduce the capacity of the evaporator under low heat load conditions.
In other attempts to reduce refrigeration capacity two or more separate refrigeration systems are employed wherein one system operates independent of the other under control of a two step thermostat. In these applications in low heat load conditions, only one system is energized with the second energized only when high heat load conditions dictate. When two separate evaporators that are arranged in the air path are employed they may be intertwined so that all of the air sees all of the refrigerant regardless of which circuit is in operation, or alternatively they may be separate heat exchangers for each circuit. In the case of intertwining evaporators of separate refrigerant circuits, poor humidity control results when only one circuit is operating due to higheroverall evaporator temperatures. In some of the cases where separate heat exchangers are employed unacceptable stratification and uneven temperature distribution have resulted when only one heat exchanger or circuit is in use since the tendency is for a greater portion of air to flow through the inoperative relatively dry evaporator which will offer less resistance to the air flow.